Pregnancy & Conception
Due Date Calculator

Just enter your information below and click on "Calculate" or scroll down first for a more thorough explanation of these terms and FAQ's about due date calculation.

Determine Pregnancy Due Date

Last Menstrual Period:        
                              (MM/DD/YYYY format)

Average Length of Cycles:      (22 to 45)
                              (defaults to 28)

Average Luteal Phase Length:   (9 to 16)
                              (defaults to 14)



Estimated Conception:         
Estimated Due Date:           
Estimated Fetal Age:          

Due Date Calculation FAQ's

What is the luteal phase?
Luteal phase is the number of days between ovulation and the start of your next period. Signs that ovulation has occurred are a spike in your basal body temperature and drying up of fertile quality cervical fluid.

(For more information about how your body works, Taking Charge of Your Fertility by Toni Weschler is an excellent manual for understanding your cycles, pinpointing problems and getting desired fertility results.)

Are there other ways to calculate due date?

• The most basic formula adds 281 days (40 weeks) to the date of your last menstrual period (LMP). Another way to arrive at the same date is to add 7 days to your LMP and subtract 3 months.
• To calculate your due date by conception date, add 267 days (38 weeks) to your date of conception.
• Ultrasound is used to estimate due date. While fairly accurate when done in the early weeks of pregnancy, ultrasound is infamously inaccurate at estimating fetal age and size later in pregnancy.
• Other ways that are sometimes used to help confirm or predict due date include using the date the heartbeat was first detected or that you first felt baby kick, and growth and measurement of the uterus.

How accurate is my birth due date?
It depends on how it was calculated as well as how much and how accurate is the information you have about your cycle around the time of conception.

The pregnancy wheel used in most doctor's offices assumes a generic 28-day cycle with ovulation at day 14. Most women don't fit this "textbook" model and many can vary quite a bit from it.

The more you know about your cycle, the more accurate your estimated due date will be. Because I had been charting my cycles and basal body temp, I was able to use that information to calculate my due dates. My firstborn even came on the due date I set!

What if my cycles are irregular?
Be as accurate as you can with your LMP, use the default settings on the conception due date calculator, and then take your due date with a big grain of salt! Even with certain dates and an accurate pregnancy and conception due date calculator, there are many factors that affect your baby's due date. It is wise to leave a wide margin and think of it more in terms of a "due month" than a specific calendar date.

My cycles were very long and irregular when I became pregnant with my first. Since I had been charting, we were able to customize my due date. Good thing, because his actual birth day would have considered over a month overdue by the generic formula!

Relax and enjoy your pregnancy and don't pay too much attention to the calendar. Your baby knows just when his or her birth day should be!

What You Should Know About Overdue Pregnancy

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